Instruments used for robotic surgery are “virtually impossible” to clean completely, according to a report published in Infection Control & Hospital Epidemiology.

“A new standard for the cleaning of complex surgical instruments needs to be established, especially for those used in robotic surgery,” wrote Yuhei Saito of the surgical center at the University of Tokyo Hospital and associates.

They assessed the residual contamination of both robotic and regular surgical instruments at their medical center because “hospital staff in central sterile supply departments are troubled by the reprocessing of robotic instruments because they cannot be disassembled for cleaning like other endoscopic instruments. Their complex structure impairs brushing the inner surface of narrow lumens, resulting in failure to [completely] remove contaminants,” the researchers wrote.

In the first phase of the study, the researchers examined 41 instruments immediately after they were used in robotic surgery (7 radical prostatectomies and 2 anterior resections of the rectum) and 27 regular instruments immediately after they were used for open surgery (gastrectomy and colectomy). The robotic instruments were contaminated with 72.3 × 103 mcg of protein each, compared with 5.5 × 103 mcg of protein on the regular instruments, the investigators reported (Infect Control Hosp Epidemiol. 2016 Oct 31. doi: 10.1017/ice.2016.249).

In the second phase of the study, the researchers examined another 24 robotic instruments and 40 regular instruments after they were used in surgery and then cleaned according to the manufacturers’ instructions three successive times. For the robotic instruments, this involved manually brushing the outer surface while moving the instrument “wrists” through their full range of motion, followed by 15 minutes of ultrasonication with enzymatic detergent, flushing the lumen with a water gun through flush ports, and rinsing the entire instrument. For regular instruments, cleaning involved washer-disinfectors and included 5 minutes of ultrasonication, 10 minutes of spraying with an alkaline detergent, and 10 minutes of disinfection via heating.

The level of contamination declined with each successive cleaning but still remained comparatively high for the robotic instruments. The amount of protein contaminants released in the three cleanings was 650, 550, and 530 mcg per robotic instrument, compared with 16, 17, and 17 mcg per ordinary instrument.

The efficacy of cleaning was 97.6% for robotic instruments and 99.1% for regular instruments, the researchers reported.

This study was not designed to assess whether residual contamination is associated with adverse events such as infection in subsequent patients, and there are few data available on this topic.

“We have to recognize that there might be a considerable volume of insufficient cleaning or occult surgical site infections,” the investigators wrote.

New instrument washers equipped with a specific cleaning function for narrow lumens are becoming available, they noted, and “further study should be conducted using these washers with improved cleaning efficacy.”

The study was supported by the Japan Society for the Promotion of Science. The investigators reported having no relevant financial disclosures.

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